The present study uses density functional theory to investigate the effects of hydrogen bonding on the (N1) acidity of uracil. Uracil and uracil anion complexes with water, ammonia, and hydrogen fluoride at various uracil sites (O2(N3), O4(N3) and O4(C5)) are considered. The calculated geometries of the uracil anion complexes are significantly different from those of the (neutral) uracil counterparts, which leads to the significantly larger binding energies in the anionic complexes. The binding strength of each molecule to (neutral) uracil is largest at the O4(N3) position and at the O2(N3) position in the uracil (N1) anion. Our calculations reveal that hydrogen-bonding interactions with one molecule increase the (N1) acidity of uracil by up to approximately 50 kJ mol(-1) and that the effect of two molecules is approximately equal to the sum of the individual effects. The acidity increase is largest when water and ammonia bind to the O4(C5) position and when hydrogen fluoride binds to the O2(N3) position. Our results lead to a greater fundamental understanding of hydrogen-bonding interactions involving uracil and have important implications for interactions in biological systems, such as those at the active site in uracil DNA glycosylase.